1. Field of the Invention
This invention relates to laser marking systems. More specifically, the present invention relates to methods and apparatus for the high speed generation of character or symbol patterns used to mark objects by means of focused laser radiation.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope thereof.
1. Description of the Related Art
Laser marking systems are known in the art. At or about the time of the filing of the present application, the Markem Corporation of Keene, N.H. was engaged in the manufacture of a system which reflected the state of the art in laser marking tools. In general, laser marking tools are used to etch an identifying symbol or set of symbols on a surface or object. In certain applications, high speed is required to make a number of marks on a number of articles of manufacture.
At least two marking techniques are known in the art. The first involves the writing of each character or symbol in a script style. The other involves the stenciling of each symbol or character by a pulsed laser beam. The stenciling technique involves the use of a mask wheel which has a peripheral template with a plurality of transmissive character or symbol pattern apertures. The mask wheel is spun into position and the laser is activated to generate the desired character at the target.
The writing technique is most often used, as it requires much less power than the stenciling technique. The stenciling technique, however, is faster. Unfortunately, there are problems with the stenciling technique that have heretofore limited its utility for the high speed applications mentioned above. For example, the high beam power required for the high speed stenciling of metallic, ceramic or glassy surfaces tends to damage the transmissive stencil. This in turn necessitates the use of large aperture patterns for stencils to reduce the radiant energy density on the aperture mask. When the resultant large diameter mask wheel is spun at high speeds coincident with high laser pulse repetition rates, centrifugal forces are generated which can cause the wheel to rupture.
Further, the marking of metals, ceramics and glassy surfaces requires laser radiation of short wavelengths to maximize energy coupling into the target thereby minimizing the total required energy. This necessitates the substitution of high temperature tolerant refractive elements in the stencil when alternate high power short wavelength laser sources are used.
There is therefore a need in the art for a high speed laser marking apparatus and technique which does not require costly maintenance and substitution of the symbol mask.